PROJECT SUMMARY ABSTRACT Laboratory alcohol challenges, in which researchers assess participants? responses to alcohol administered in a controlled setting, have provided the alcohol research community with important knowledge about the associations between individual responses to alcohol and risk for drinking-related problems. In recent studies in young adult heavy drinkers, our group showed that greater sensitivity to alcohol?s stimulant and rewarding effects was more predictive of future development of alcohol use disorder (AUD) symptoms than were lower responses to sedative or intoxicating effects. While laboratory-derived alcohol challenges remain the ?gold standard? for measuring alcohol responses, the time- and resource-intensive nature of this approach has hampered efforts to extend findings of alcohol challenge studies to intervention and epidemiological research. One potential solution to this problem is to develop and validate an accessible and user-friendly method to measure alcohol responses outside of the laboratory using ecological momentary assessment (EMA). EMA methods assess individuals? behaviors and experiences in real-time and in their natural environment. Rapid advances in mobile smartphone technology and high adoption rates of these devices (86% of young adults own a smartphone) suggest that EMA alcohol response data may be collected via this portable and user- friendly method, e.g., providing data via text messaging and mobile web from one?s own smartphone. Our pre- pilot work suggests that using smartphones to measure alcohol responses in vivo is reliable, safe, and well- received by young adult heavy drinkers. The goal of this proposal is to build on this to further establish the reliability, validity, and safety of a smartphone-based EMA technique for measuring alcohol responses in drinkers? natural environments, and to examine associations with identical measures obtained via laboratory alcohol challenge. We plan to collect alcohol response data during at least 2 real-world drinking episodes from 64 young adult heavy drinkers (ages 21-29), and compare these responses with those obtained during a laboratory alcohol challenge. Safety of the smartphone procedure will be assessed by next-day and 2-week follow-up assessments of alcohol use and consequences, and by comparing those outcomes to a sample of n=20 heavy drinkers who will also complete these measures but not the smartphone/laboratory assessments. Estimated breath alcohol content (eBrAC) will be calculated during the smartphone-based assessments and actual BrAC will be measured during the laboratory challenge. Both the laboratory- and smartphone-based assessments will assess subjective alcohol stimulation, sedation, and reward (liking and wanting) using brief (~1 min), psychometrically sound measures. The results will contribute to knowledge on individual differences in alcohol responses in the natural environment. If shown to be reliable, valid, and safe, this new smartphone- based EMA technique could be used to inform future research on AUD risk assessment and treatment, as well as population-based work to examine changing patterns of drinking behavior and responses.